Continuous casting apparatus for shaped metal bodies

ABSTRACT

A slag bath is formed in the upper portion of a molding cavity formed between casting molds. Molten metal is poured into the molding cavity through the slag bath. Viscous slag films are formed by the slag bath between the casting molds and the metal. The metal is cooled through the slag films.

Patented Aug. 14, 1973 4 Sheets-SheenI 1 TIG] INVENTOR KIYOSHIGE TORIKAI BY www@ ATTORNEYS Patented Aug. 14, 1973 3,752,215

4 Sheets-Sheet 2 INVENTOR KlYOSl-HGE TOIIKAi ATTORNEY,

Patented Aug. 14, 1973 3,752,215

' 4, Sheets-Sheet 5 ITIGJA INVENTOR KIYOSHIGE TORIKAI BY M/m ATTORNEYS Patented Aug. 14, 1973 3,752,215

4 Sheets-Sheet 4 INVENTOR KIYOSH IGE TORIKAI BY /M/f M ATTORNEYS CONTINUOUS CASTING APPARATUS FOR SHAPED METAL BODIES BACKGROUND OF THE INVENTION The present invention relates to a continuous method and apparatus for casting hollow metallic shaped body ies (eg. metal tubes, pipes, etc.) or solid metallic shaped bodies (e.g. structural members having irregular cross sections, such as metal rods, rolls, channel materials, etc.), and more particularly to a method and apparatus suitable for the continuous casting of steel materials.

Various systems have heretofore been proposed for the continuous casting of hollow metallic shaped bodies, e.g. steel tubes. However, these systems are without exception based on the concept of obtaining the products by using a water-cooled outer casting mold for forming a solidified shell constituting the outer wall of a steel tube and a water-cooled inner casting mold for forming a solidified shell constituting the inner wall of the steel tube, continuously pouring a molten metal into the molding cavity formed by the gap between the two casting molds from the upper side, continuously forming solidified metal shells by the cooling action of the inner and outer casting molds to form a tubular body and successively drawing the tubular body downwardly. Since these conventional systems have many technically unsolved problems as will be set forth below, this type of continuous casting technique has not been satisfactorily developed. The above-mentioned technically unsolved problems are:

l. The prevention of the melt-bonding (interdiffusion of metallic atoms) phenomenon occurring between the molten metal (melt) and the casting mold.

2. The elmination of tightening force exerted by the solidified metallic shell on the inner casting mold due to contraction of the shell under the cooling action of the casting molds.

3. Since the casting molds and the molten metal are in contact with each other either directly or through a very thin layer of a lubricant (flux), the molten metal is cooled rapidly by the casting molds. This makes it very difficult to control the solidification of the molten metal, and thus the position of solidification of the molten metal in the molding cavity varies greatly and is indefinite. When the solidifying position moves upwardly toward the upper portion of the molding cavity, the solidified shell due to contraction thereof strongly tightens against the inner casting mold. n the other hand, when the solidifying position moves downwardly toward the lowerportion of the molding cavity, conversely, the shell is insufficiently solidified, whereby the shell is susceptible to splitting or cracking with the resultant danger of blow out of the molten metal. Thus, a further unsolved problem of prior systems is the controlling of the speed of cooling of the molten metal by the casting molds to maintain the solidification conditions of the molten metal constant.

A number of solutions have been proposed to solve the above problems. However, all of these proposals have for various reasons failed to provide completely satisfactory results.

For instance, in one presently used system for the continuous casting of solid steel bars, an attempt is made to solve the above-mentioned problems by im parting vibration or vertical movement to the casting molds or by adding a flux (lubricant). However, it is well-known that the blow out of molten metal is still frequently encountered and many surface defects, e.g. scratches, wrinkles and cracks, occur in the finished products. Therefore, as may be readily understood, it would be almost impossible to control the inner casting mold tightening action of the inner surface of the solidified shell contracting with the passage of time if the above means were applied to a method for the continuous casting of hollow shaped metallic bodies. It has also been proposed, in the continuous casting of hollow shaped metallic bodies, to regulate the thickness of the solidified shell, i.e.' the thickness of a hollow metallic shaped body, without using the inner casting mold. According to this method, however, it is impossible to obtain a product of accurate thickness and hence such method is impractical.

OBJECTS AND BRIEF DESCRIPTION OF THE INVENTION With the above disadvantages in mind, it is an object of the present invention to provide a method and apparatus by which hollow shaped metallic bodies may be easily and accurately continuously molded.

It is a further object of the present invention to provide a method and apparatus by which hollow and solid shaped metallic bodies free of surface defects can be continuously molded without blow out of the molten metal.

These objects are achieved in accordance with the present invention by the provision of a method and apparatus wherein a molten metal is continuously poured at a predetermined rate into a molding cavity from the upper side thereof, and a solidified metallic shell is continuously formed in the molding cavity by the cooling action of casting molds, whereby a metallic shaped body is continuously formed. The metallic shaped body is continuously drawn downwardly to thereby obtain a metallic shaped body of a desired shape. In the upper portion of the molding cavity is formed a slag bath having a relatively large depth, a high temperature and good flowability by means of electric resistance heat. The molten metal is poured into the molding cavity through the slag bath.

Other objects, features and advantages of the present invention will be made apparent by the following detailed description together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a schematic illustration, with parts broken away and shown in cross section, of an embodiment of the present invention;

FIGS. 2(A) and 2(8) are top views schematically illustrating arrangements for forming hollow shaped metallic articles in accordance with 'the present invention;

FIGS. 3(A) and 3(8) are top views schematically illustrating arrangements for forming solid shaped metallic `articles in accordance with the present invention; and

FIGS. 4-6 are schematic illustrations, with parts broken away and in cross section, of modified embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION l With reference now to the drawings, the present invention will be described in detail.

ln FIG. l, reference numeral I designates-awatercooled outer casting mold, and 2 designates a watercooled inner casting mold (core). The gap between these casting molds l and 2 forms a molding cavity in which the hollow shaped metallic body is to be continuously cast. Reference numeral 3 designates a nonconsumable electrode arranged above the gap between the casting molds l and 2, i.e. the molding cavity, with the lower end thereof projecting a suitable distance into the cavity. Reference numeral 4 designates a frame for holding the non-consumable electrode 3 and which is constructed to be cooled by water or air. Reference numeral 5 designates a power source slidably electrically connected to the molded body 12 and electrically connected as shown in FIG. 1 to supply a large current Ato the non-consumable electrode 3, so that a slag bath 8 to be described later may be heated by the electric resistance heat of the non-consumable electrode and maintained at about 1,500C. 2,000C. and thus in a highly flowable state. Reference numeral 6 designates a tundish for storing molten metal received from a ladle. The tundish 6 is arranged above the casting molds 1 and 2, and provided in the bottom portion thereof,

above the gap between the casting molds l and 2, is av of the fixed type since the local temperature change of the molten metal in the molding cavity is small due to the heat insulating effect of slag films l0 to be described later. Reference numeral 7 designates a heatresistant protective tube connected to the discharge opening of the nozzle 6a and extending from the discharge opening to a point adjacent the top end of the molding cavity. The protective tube 7 serves to prevent the molten metal, flowing downwardly from the nozzle 6a, from expanding outwardly.

ln FIG. 2(A) there is shown a plan view of the device of FIG. l, but wherein three nozzles 6a are equally spaced around the molding cavity, and wherein three non-consumable electrodes 3 are similarly equally spaced therearound. FIG. 2(B) represents a modification of the arrangement of FIG. 2(A) and shows only two nozzles 6a, but six non-consumable electrodes 3.

In FIG. 3(A) there is shown a plan view of an arrangement for the formation of a solid shaped metallic body wherein two nozzles 6a and three nonconsumable electrodes 3 are employed. FIG. 3(8) is similar to FIG. 3(A), but shows the use of a total of l2 non-consumable electrodes 3.

It is to be understood that the number of nozzles and the number of non-consumable electrodes may be varied as desired.

Reference numeral 8 designates a slag bath located in the upper portion of the molding cavity, and the composition of which may be optional provided that it can be heated by electric resistance and is highly flowable. For instance slag bath 8 may be of the type used in ordinary electroslag melting. Reference numeral 9 designates a metal bath which is formed after the molten metal supplied from the nozzle 6a of the tundish 6 has passed through the slag bath 8 formed in the upper portion of the molding cavity. The upper surface of the metal bath 9 is always maintained at a high temperature by the slag bath 8. Reference numeral l0 designates slag films naturally formed on the surfaces of the casting molds when the slag bath 8 flows downwardly along the surfaces thereof while being cooled. The slag films 10 are relatively small in thickness and highly viscous, and perform a lubricating action between the casting molds and a solidified shell l1 to be described later, a protective action against the constraction of the solidified shell ll and a slow-cooling action. The slag bath 8 is always sufficiently heated by the electric resistance heat and is highly flowable as described above. The temperature and depth of the slag bath 8 and the amount of heat cooled by the casting molds can be freely adjusted by the amount and temperature of cool ing-water supplied to molds l and 2 by cooling-water supplies 1a and 2a, respectively. Therefore, the thickness of the slag films 10 can also be controlled. According to experiments, it has been found that slag films l0 of 0.2 2.0 mm in thickness can be obtained.

Reference numeral 11 designates the solitified shell continuously formed as a result of the metal bath 9 being cooled by the casting molds through the abovementioned slag films l0 which are naturally formed on the surface of theV casting molds. Since the solidified shell ll is cooled by the casting molds through the slag films l0 as stated above, the amount of heat absorbed by the casting molds is relatively small and hence the solidified shell is formed relatively slowly and the position-of solidfication thereof will not rapidly change or substantially vary. Further, since the solidified shell is surrounded by the viscous slag films l0, it will not be melt-bonded to the casting molds nor will it tighten the inner casting mold 2 as in previous molding methods. Reference numeral 12 designates a hollow metallic shaped body continuously formed as a result of the solidified shell ll being further cooled by the casting molds. The hollow metallic shaped body l2 is drawn out of the casting molds downwardly by pinch rolls or other conventionally known suitable drawing means (not shown) provided below the casting molds, at a rate suitable to maintain the surface of the metal bath 9 at a constant level. Reference numeral 13 designates secondary cooling means provided below and adjacent the casting molds. By the water supplied through pipes 13a and 13b and jetting from the cooling means 13, the hollow metallic shaped body l2 is cooled and the slag'films l0 attached to the inner and outer peripheral surfaces thereof are removed in the vicinity of the outlet end of the molding cavity. The cooling of the hollow metallic shaped body l2by the secondary cooling means 13 does not have any detrimental effect on the slag films 10 at the portion where the molten metal starts to form the solidified shell 1 l, but rather brings about such desirable result as increasing the thickness of the solidified shell ll at the lower portion of the molding cavity and shortening the range in which the molten metal is solidified. Where the thickness of the shaped body to be cast is large, this secondary cooling is necessary because the amount of heat absorbed by the casting molds from the molten metal is relatively small as stated above.

The mode of practicing the present invention will now be described with reference to FIG. l. In conducting the continuous casting operation according to the invention, a start piece is first inserted into the molding cavity from the lower side thereof as in conventional methods, and the material to form the slag bath 8 is heated in a separate crucible by electric resistance heat to form a molten slag. The molten slag thus formed is poured into the upper portion of the molding cavity to form the slag bath 8. It is preferable that the depth of the slag bath is generally on the order of about 30-80 mm. The temperature can be easily adjusted and the heat capacity can be maintained at a suitable level. After the slag bath 8 has been formed in the upper portion of the molding cavity in the manner described, the molten metal is fed from the nozzle 6a of the tundish 6 into the molding cavity at a predetermined rate and the start piece is continuously lowered. Thereby, the molten metal moves down through the slag bath 8 and forms the metal bath 9. ln this case, part of the slag bath 8 has already been cooled by the casting molds and the viscous slag films l0 have been formed on the surfaces of the casting molds. Therefore, the metal bath 9 formed in the manner described is cooled through the slag films 10 and continuously forms the solidified shell 11. The solidified shell 11 is further cooled by the casting molds and the hollow metallic shaped body l2 is continuously formed and drawn out downwardly by the drawing means.

Since the upper surface of the metal bath 9 is always maintained at a high temperature by the high temperature of slag bath 8, the shape of the solidified shell 1l will not be caused to change rapidly due to a rapid change of the axial temperature gradient or other thermal conditions, and hence the position of solidification of the shell can be easily controlled. Furthermore, the slag films 10 present between the solidified shell and the hollow metallic shaped body l2 and the casting molds provide lubrication between the casting molds and the solidified shell ll, protect the solidified shell ll against contraction and cause the solidified shell 11 to cool slowly. Therefore, the solidified shell ll is formed relatively slowly and the position of solidification thereof does not shift as stated above. Further, the molten metal is not melt-bonded to the casting molds nor does it tighten the inner casting mold 2. The hollow metallic shaped body 12 formed and drawn in the manner described has the slag l0 detached from the inner and outer surfaces thereof and is further cooled by the jets of water from the secondary cooling means, and is thus taken out as a finished product.

As will be clearly understood from the foregoing description, the continuous casting system of the present invention is characterized by the following advantages:

i. Since the slag films 10 are always present between the molten metal and the casting molds, there is no danger of the molten metal and the casting molds being meltbonded with each other.

ii. Owing to the protective action of the slag films l0 against the contraction of the solidified shell 11, the solidified shell ll does not tighten the inner casting mold 2.

iii. Since the molten metalforrns the solidified shell 1l by being cooled by the casting molds through the slag films 10, the cooling speed of the molten metal is relatively slow as compared with conventional methods and hence a rapid shifting and the solidifying position does not occur. That is, it is easy to control solidification conditions and, therefore, the inner casting mold 2 is not tightened by the solidified shell l1 and the solidified shell 1l is not split or cracked, and the danger of the molten metal becoming blown out is eliminated.

iv. Since the upper surface of the metal bath 9 is always maintained at a high temperature, the axial temperature gradient or other thermal conditions are not subject to a rapid change, and thus the shape of the solidified shell is not rapidly changed. Therefore, the controlling of the solidification position is made easy.

v. Since the molten metal is poured into the molding cavity through the deep slag bath 8, there is no danger of splashing or oxidation and, therefore, the use of a sink nozzle is unnecessary.

vi. Since the slag films l0 present between the solidified shell ll and the hollow metallic shaped body l2 and the casting molds provide lubrication therebetween, the hollow metallic shaped body l2 can be smoothly drawn out, thus eliminating the formation of flaws and other defects occurring on the surface of the shaped metallic body.

Thus, the present invention provides a novel solution to all of the heretofore unsolved problems previously set forth.

Another embodiment of the present invention is shown in FIG. 4 and diers from that shown in FIG. l in that cooling means 14 is provided integrally at the lower portion of the casting molds for cooling that portion of the solidified shell ll by injecting air or water into a slight gap formed by the contraction thereof. Such an arrangement has the advantage that the cooling speed of the shaped body l2 can be automatically adjusted in proportion to the size of the gap. ln this case, the hot air or aqueous vapoi generated in the gap does not have any detrimental effect on the solidified shell l1 and the shaped body l2, since the solidified shell ll and the shaped body -12 are surrounded and protected by the slag films l0.

Other embodiments of the invention as shown in FIGS. 5 and 6 and are adapted particularly for continuous casting of shaped bodies of small thicknesses and differ from the embodiment of FIG. l in that a graphite lining l5 is provided on a portion only (in case of FIG. 5) or on the entire surface (in case of FIG. 6) of the inner wall of each casting mold, thereby to further slow down the cooling speed of the molten metal. In this case, since the cooling speed of the molten metal is further reduced by the graphite lining l5 as mentioned above, there is the additional advantage that the position of solidification and the cooling speed may be easily controlled, even when the shaped body is thin. Hence the casting of a thin shaped body can be easily achieved. ,f

Although all of the above specifically described ernbodiments have involved the continuous casting of hollow shaped metallic bodies, it will be obviously understood that the present invention is equally applicable to the continuous casting of solid shaped metallic bodies. Namely, in the casting of solid shaped metallic bodies, it is only'necessary to eliminate the inner casting mold (core), and for obtaining solid shaped bodies of irregular cross sections it is only necessary to suitably design the cross-section shape of the moldingcavity to conform with the cross-sectional shape of the body to be molded.

Although preferred embodiments of the invention have been described in detail, such description is intended to be illustrative only, and not restrictive, since many details of the construction of the invention may be altered or modified without departing from the spirit or scope of the invention.

What is claimed is:

l. In an apparatus for continuously casting shaped metallic bodies including casting molds forming therebetween a molding cavity and means positioned above said molding cavity for pouring molten metal therein, said molten metal solidifying by contact with said casting molds; the improvement comprising a slag bath positioned in the upper portion of said cavity; means for maintaining said slag bath at a high temperature and in a liquid state, said means comprising at least one nonconsumable electrode means mounted in at least one predetermined position dependent upon the shape of said shaped bodies for heating said slag both by electric resistance heat; and means separate from said electrode means for depositing said molten metal directly on top of said slag bath, whereby said molten metal passed through said slag bath.

2. The improvement claimed in claim l, further comprising viscous slag films formed from said slag bath and positioned between said casting molds and said metal.

3. The improvement claimed in claim l, further comprising means positioned adjacent the lower portion of said molding cavity for directing a fluid against the surfaces of said solidified metalv to provide further cooling thereof.

4. The improvement claimed in claim 3, wherein said fluid directing means are integral with said casting molds.

5. The improvement claimed in claim l, further comprising a graphite lining positioned in the upper portion of said molding cavity.

6. The improvement claimed in claim l, further comprising a graphite lining positioned in said molding cavity. 

1. In an apparatus for continuously casting shaped metallic bodies including casting molds forming therebetween a molding cavity and means positioned above said molding cavity for pouring molten metal therein, said molten metal solidifying by contact with said casting molds; the improvement comprising a slag bath positioned in the upper portion of said cavity; means for maintaining said slag bath at a high temperature and in a liquid state, said means comprising at least one non-consumable electrode means mounted in at least one predetermined position dependent upon the shape of said shaped bodies for heating said slag both by electric resistance heat; and means separate from said electrode means for depositing said molten metal directly on top of said slag bath, whereby said molten metal passed through said slag bath.
 2. The improvement claimed in claim 1, further comprising viscous slag films formed from said slag bath and positioned between said casting molds and said metal.
 3. The improvement claimed in claim 1, further comprising means positioned adjacent the lower portion of said molding cavity for directing a fluid against the surfaces of said solidified metal to provide further cooling thereof.
 4. The improvement claimed in claim 3, wherein said fluid directing means are integral with said casting molds.
 5. The improvement claimed in claim 1, further comprising a graphite lining positioned in the upper portion of said molding cavity.
 6. The improvement claimed in claim 1, further comprising a graphite lining positioned in said molding cavity. 